An integrated circuit includes two, three or more levels of conductors that extend across the topography of a monolithic substrate. A via is etched through the dielectric layer on the conductor that is in or on an underlying dielectric layer in the contact structure. Typically, an etch stop layer is applied over the underlying dielectric layer to assure the etching process stops on a etch stop layer. The via is filled with a conductive material to form a plug.
Inside the via from at a top surface of the conductor, an exposed portion of the etch stop layer is etched away so as to further expose the top surface of the conductor. In removing the etch stop layer over the conductor, the exposed top surface of the conductor, like a conductive metal, is apt to react with oxygen to form a porous metal oxide layer having a higher electric resistance.